1. Technical Field
The present disclosure relates to a wiring substrate on which an electronic component such as a semiconductor chip is mounted.
2. Description of the Related Art
In the related art, there is a wiring substrate on which an electronic component such as a semiconductor chip is mounted. In an example of the wiring substrate, a built-up wiring layer is formed on one surface or both surfaces of a core substrate according to a semi-additive method.
In recent years, a narrower pitch of a wiring layer of the wiring substrate has been developed according to high performance of an electronic component such as a semiconductor chip (see e.g., JP-A-61-113296, JP-A-2002-252459 and JP-A-2009-188429).
As described in the following section of preliminary matters, in a case of forming a multilayer wiring structure using the semi-additive method, a surface of an insulating resin layer is roughened by etching when a desmear process is performed on the inside of a via hole. Thus, a wiring layer can be formed on the insulating resin layer with good adhesion due to an anchor effect.
In recent years, there has been a demand for making a wiring layer finer in a wiring substrate according to miniaturization and high performance of a semiconductor chip.
If a surface of an insulating resin layer is uneven, particularly, if a pitch of a wiring layer is narrowed, a residue tends to occur when a seed layer is etched, and thus wiring layers are easily electrically short-circuited to each other. In addition, there is a problem in that a transmission loss of a high frequency signal tends to occur in a wiring layer formed on the uneven insulating resin layer.
As such, in the method of roughening the surface of the insulating resin layer so as to secure adhesion of the wiring layer with respect to the insulating resin layer, it is difficult to form a wiring layer having the line width of 10 μm or less with high reliability, and a technique is required in which a fine wiring layer is formed on a smooth resin layer with good adhesion.